The molecular properties and kinetic characteristics of various enzymes involved in the metabolism of S-adenosylmethionne have been investigated. 5'-Methyl-thioadenosine nucleosidase from lupin seeds has been purified to homogeneity, and the molecular weight, subunit and kinetic characteristics of the enzyme has been investigated. The irreversible inhibition and substrate specifies of S-adenosylhomocysteinase from various sources have been investigated in considerable detail. S-Adenosylhomocysteinase from hamster liver has been purified to homogeneity and its kinetic characteristics, and sensitivity to inhibitors has been compared to that of the enzymes from beef liver, previously crystallized by Chiang, Richards and Cantoni.